The present disclosure relates to subject matter contained in Japanese Patent Application No. 10-259775 (filed on Sep. 14, 1998), which is expressly incorporated herein by reference in its entirety.
1. Field of the Invention
The present invention relates to a snare that is inserted into an instrument-inserting channel of an endoscope to excise a polyp.
2. Description of the Prior Art
FIG. 5 shows a distal end portion of a conventional snare for use with an endoscope. In a flexible sheath 1, a control wire 2 is axially movably inserted, and a snare loop 3 formed by an elastic wire is connected to the distal end of the control wire 2 through a connecting pipe 4.
At the distal end of the snare loop 3, a single elastic wire is bent back in a U-shape as shown in FIG. 5. Alternatively, two elastic wires are inserted into a binding pipe (not shown) so as to be secured together therein.
By virtue of the above-described arrangement, the snare loop 3 projects from or withdraws into the distal end of the flexible sheath 1 in response to an operation of advancing or retracting the control wire 2 in the axial direction. When projecting from the distal end of the flexible sheath 1, the snare loop 3 expands in a loop shape by its own elasticity. When pulled into the distal end of the flexible sheath 1, the snare loop 3 is folded.
To excise a polyp with the snare, the base of the polyp is encircled with the snare loop 3 expanded by being pushed out from the distal end of the flexible sheath 1. In this state, the control wire 2 is pulled toward the proximal end of the flexible sheath 1 (rightward as viewed in FIG. 5).
Consequently, the snare loop 3 is gradually pulled into the flexible sheath 1 while reducing the loop size, causing the polyp to be pinched tight with the snare loop 3. If a high-frequency electric current is supplied to the snare loop 3 through the control wire 2 in this state, the polyp is cut off without bleeding.
In the conventional snare for an endoscope having the above-described structure, however, the inner diameter d of the flexible sheath 1 must be larger than the outer diameter of the connecting pipe 4, which connects together the control wire 2 and the two portions of the single elastic wire or the two elastic wires that constitute the snare loop 3. In a case where the width W of the distal end portion of the snare loop 3 is larger than the outer diameter of the connecting pipe 4, the inner diameter d of the flexible sheath 1 must be larger than the width W.
Consequently, the inner diameter of the flexible sheath 1 becomes considerably large. Therefore, when the control wire 2 is pulled to pinch a polyp tight with the snare loop 3, the polyp may be undesirably drawn into the flexible sheath 1. This may hinder the polyp excision treatment.